Field of the Invention
The invention relates to an assembly including a device for holding a sheet on a cylinder participating in a reversal of the sheet in a sheet-processing machine.
The published European Patent Document EP 0 306 684 A2 discloses a so-called single-drum sheet-reversing or turning device in a sheet-fed rotary printing machine, wherein a sheet printed on a first side thereof is picked up directly from an upline impression cylinder by a sheet reversing or turning cylinder and, after having been reversed or turned, is transferred to a succeeding impression cylinder.
A blowing or blast device arranged directly upline from the pick-up or take-over location between the upline impression cylinder and the sheet reversing cylinder presses the sheet by blown or blast air onto the surface of the impression cylinder in a region upline from the pick-up location, in order to improve the in-register action of picking up the sheet from the impression cylinder.
By arranging the blowing device upline from the location at which the sheet is transferred from the upline impression cylinder to the sheet reversing or turning cylinder, as viewed in the sheet transport direction, the holding force on the end of the sheet becomes ineffective before the sheet end is picked up by the gripper device of the sheet reversing or turning cylinder.
Especially at machine speeds below the minimum production printing speed, such as during inching or crawling, and braking the machine during an emergency stop and subsequent re-starting, the end of the sheet is not adequately held, so that faults in the turning or reversing register may occur. In the worst case, a sheet can even be lost as it is being turned, i.e., the sheets which are released fall into the machine.
It is accordingly an object of the invention to provide a device for holding a sheet on a cylinder participating in a reversal of the sheet in a sheet processing machine, wherein the sheet is held on the cylinder in all possible operating conditions, so that a problem-free paper run is possible.
With the foregoing and other objects in view, there is provided, in accordance with the invention, an assembly including a device for holding a sheet on a cylinder participating in a reversal of the sheet, comprising a region wherein the holding device is effective for holding a sheet, the effective region for the holding device being located downline, as viewed in a sheet transport direction, from an upline effective region wherein the sheet is gripped by a lifting device.
In accordance with another feature of the invention, the holding device is constructed as an activatable holding roller.
In accordance with a first alternative feature of the invention, the holding device is constructed as a blowing device.
In accordance with a second alternative feature of the invention, the holding device is constructed as a guiding device.
In accordance with a third alternative feature of the invention, the holding device is a combination of a holding roller and a blowing device.
In accordance with a fourth alternative feature of the invention, the holding device is a combination of a holding roller and a guiding device.
In accordance with a fifth alternative feature of the invention, the holding device is a combination of a blowing device and a guiding device.
In accordance with a sixth alternative feature of the invention, the holding device is a combination of a holding roller, a blowing device and a guiding device.
In accordance with a further feature of the invention, the assembly includes a plurality of blowing devices provided for holding the sheet on the cylinder.
In accordance with a concomitant feature of the invention, the cylinder is an impression cylinder of a sheet-fed rotary printing machine, and the lifting device is mounted on a reversing or turning drum so as to be extendable.
An advantage of the invention is that the sheets to be turned or reversed are reliably held even at low machine speeds and even downline of the transfer location.
The construction of the holding device as a pressure roller is particularly advantageous. A pivotable mounting permits the pressure roller to be brought into and out of contact from an out-of-contact or disengaged position for production printing into an in-contact or engaged position on the cylinder in a speed range below the minimum production printing speed.
The pressure roller can preferably be employed for all thicknesses of paper from thin bible paper up to thick cardboard or pasteboard.
In an alternative configuration, in particular for processing thin paper thicknesses, the holding device is constructed as a blowing device, which directs a blown-air or blast-air holding jet onto the sheet, so that the latter is pressed against the upline cylinder. In this regard, a blown or blast jet device which is oriented counter to the travel or transport direction of the sheet is particularly beneficial. This measure avoids any necessity for blowing underneath the sheet at the trailing edge thereof.
In a further alternative configuration, in particular for processing thick paper thicknesses, a guiding device is provided which is constructed as a guide bracket or guide plate and has a tip extending into a region downline from the take-over location. A pivotable mounting permits the guide bracket or the guide plate to be adjusted with respect to the impression cylinder so that spacing between the guiding device and the impression cylinder narrows in the sheet transport direction. Due to the inherent stress in thicker cardboard or pasteboard, it has the property of resting against the guiding device. A result thereof, in particular in the region of the tip of the guiding device, is that the cardboard or pasteboard sheet is held firmly on the cylinder in the transfer position even when the machine is operating slowly or is at a standstill. Due to the adjustability of the guiding device by a setting or adjusting device that is provided, the spaced distance of the guiding device from the cylinder can be set as a function of the thickness of the printing material (cardboard or pasteboard) to be processed. The trailing edge of the sheet can thereby be guided in a controlled manner by the guiding device.
While the guiding device for thick-paper thicknesses and the blowing device for thin-paper thicknesses remain continuously in the position thereof on the cylinder, both during production printing and at crawl, provision is made for the pressure roller to be connected in and activated, respectively, only at a predetermined machine speed.
A combination of pressure roller and guide bracket, or pressure roller and blowing device, or guide bracket and blowing device improves the action or effect of the device according to the invention.
The combination of a pressure roller, a blowing device and a guide bracket constitutes the optimum in functionally technical terms.
In a device for turning or reversing a sheet in a sheet-fed rotary printing machine, provision is made to transfer a sheet directly, after it has been turned or reversed, from an upline impression cylinder to a downline impression cylinder by a turning or reversing device.
In order that the sheet be held properly on the cylinder during the turning or reversing operation, in particular at a slow speed lying below a minimum production printing speed, one or more holding devices are provided, which are arranged in an effective region which, as viewed in the sheet transport direction, is located downline of an effective region for the lifting device of the turning or reversing drum.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for holding a sheet on a cylinder participating in a reversal of the sheet in a sheet-processing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: